Bump structures for interconnecting focal plane arrays

ABSTRACT

A method of forming bump structures for interconnecting components includes dry etching a layer of insulating material to create a pattern for bump structures. A seed layer is deposited on the insulating material over the pattern. The seed layer is patterned with a photo resist material. The method also includes forming bump structures over the seed layer and the photo resist material with a plating material to form bump structures in the pattern, wherein the bump structures are isolated from one another.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.15/289,627 filed Oct. 10, 2016 which is incorporated by reference hereinin its entirety.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present disclosure relates to interconnections, and moreparticularly to bump structures for electrically interconnectingcomponents such as in interconnecting focal plane array components.

2. Description of Related Art

Fine pitch, large format focal plane arrays (FPAs), require smallinterconnect bumps with large height to diameter ratios and minimumlateral expansion after hybridization. The size and height to diameterratio make the alignment difficult when interconnecting components withtraditional techniques. Additionally, lateral expansion of the bumpsaffects the pressing process and manufacturing yield. As a result,lateral expansion limits the pitch size.

The conventional techniques have been considered satisfactory for theirintended purpose. However, there is an ever present need for improvedbump structures for interconnecting components like focal plane arrays.This disclosure provides a solution for this problem.

SUMMARY OF THE INVENTION

A method of forming bump structures for interconnecting componentsincludes dry etching a layer of insulating material to create a patternfor bump structures. A seed layer is deposited on the insulatingmaterial over the pattern. The seed layer is patterned with a photoresist material. The method also includes forming bump structures overthe seed layer and the photo resist material with a plating material toform bump structures in the pattern, wherein the bump structures areisolated from one another.

The method can include removing the photo resist material after formingbump structures over the seed layer and the photo resist material.Removing the photo resist material can include leaving the bumpstructures seated in a seat of the seed layer, wherein the seed layer isrecessed below the insulating material to provide a gap between the bumpstructures and the insulating material. The method can also includepressing the bump structures and laterally expanding the bump structuresinto the gap to keep the bump structures from electrically shortcircuiting with one another.

Dry etching a layer of insulating material can include patterning theinitial layer of photo resist material, dry etching a dielectric layerdeposited between the insulating material and the initial layer of photoresist material, and the insulating material to create the pattern forbump structures. Depositing the seed layer can include depositing theseed layer over the dielectric layer, over a wafer supporting theinsulating material, and over the insulating material. The seed layercan be deposited on the wafer at a base portion of the pattern, whereinthe seed layer is deposited on the dielectric layer at a surface of thepattern opposite of the base portion, and wherein the seed layer isdeposited on the insulating material in sidewalls of the pattern. Thepattern can include holes for accommodating the bump structure, whereinforming bump structures over the seed layer and the photo resistmaterial with a plating material includes depositing plating materialonly in the holes. Forming bump structures over the seed layer and thephoto resist material with a plating material can include plating with aplating material including at least one of copper or indium.

A system includes a layer of insulating material with holes therein. Aseed layer is seated within the holes, wherein the seed layer isrecessed below a surface of the insulate material. A respective bumpstructure is seated in the seed layer of each hole. The bump structurescan be on one of a photodiode array (PDA) or a read-out integratedcircuit (ROIC), e.g., wherein the PDA and ROIC are joined together bythe bump structures. The PDA and ROIC can define a plurality of pixels,wherein the plurality of pixels have a pitch size, wherein the pitchsize is less than 10 μm. The bump structures can each have a diameterless than 5 um. The bump structures can each have a height to diameterratio of greater than 1:1.

These and other features of the systems and methods of the subjectdisclosure will become more readily apparent to those skilled in the artfrom the following detailed description of the preferred embodimentstaken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

So that those skilled in the art to which the subject disclosureappertains will readily understand how to make and use the devices andmethods of the subject disclosure without undue experimentation,preferred embodiments thereof will be described in detail herein belowwith reference to certain figures, wherein:

FIG. 1 is a schematic cross-sectional elevation view of an exemplaryembodiment of a system constructed in accordance with the presentdisclosure, showing the insulating material on a wafer before etching;

FIG. 2 is a schematic cross-sectional elevation view of the system ofFIG. 1, showing the insulating material after etching the holes;

FIG. 3 is a schematic cross-sectional elevation view of the system ofFIG. 1, showing the seed layer deposited over the insulating materialand holes;

FIG. 4 is a schematic cross-sectional elevation view of the system ofFIG. 1, showing the photo resist patterned on the seed layer;

FIG. 5 is a schematic cross-sectional elevation view of the system ofFIG. 1, showing the plating material plated into the holes; and

FIG. 6 is a schematic cross-sectional elevation view of the system ofFIG. 1, showing the bump structures remaining after removing the photoresist material.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made to the drawings wherein like referencenumerals identify similar structural features or aspects of the subjectdisclosure. For purposes of explanation and illustration, and notlimitation, a partial view of an exemplary embodiment of a system inaccordance with the disclosure is shown in FIG. 1 and is designatedgenerally by reference character 100. Other embodiments of systems inaccordance with the disclosure, or aspects thereof, are provided inFIGS. 2-7, as will be described. The systems and methods describedherein can be used to provide improved bump structures, e.g., toaccommodate smaller pixel pitch sizes in read-out integrated circuits(ROICs), photodiode arrays (PDAs), and smaller scale interconnections inother electronic assemblies.

System 100 is shown in FIG. 1 including an insulating material 102, e.g.of a polyimide or other suitable material, deposited on a wafer 104. Adielectric layer 106, e.g., of SiN or other suitable material, isdeposited on the insulating material 102, and an initial layer of photoresist 108 is deposited on the dielectric layer 106. This initialstructure can be used in a method of forming bump structures forinterconnecting components. As shown in FIG. 2, the photo resist 108 ispatterned, the dielectric layer 106 and insulating layer 102 are etched,e.g., by dry etching, to form holes 110 in the insulating material 102.The holes 110 provide a pattern 120 for bump structures 116 shown inFIG. 6. Dry etching the layer of insulating material 102 includes dryetching the dielectric layer 106.

The initial photo resist 108 is removed, and as shown in FIG. 3, a seedlayer 112 is deposited on the insulating material 102 over the pattern,e.g., over the dielectric layer 106 and holes 110 in the insulatingmaterial 102. The seed layer 112 is deposited on the surface of thedielectric layer 106, e.g., on the top surface 128 of the hole pattern120 of FIG. 2, on the sidewalls 130 of the holes 110, e.g., in directcontact with the insulating material 102, and on the bottom surface 132of the holes 110 or base portion 126 of the pattern, e.g., in directcontact with the wafer 104. As shown in FIG. 4, the seed layer 112 ispatterned with a second application of photo resist material 114. Seedlayer 112 has the properties that allow for plating bump structures ontosystem 100 as explained below with reference to FIGS. 5-6.

With reference now to FIG. 5, with the photo resist material 114patterned on seed layer 112, a plating material is plated over the seedlayer 112 and the photo resist material 114 to form bump structures 116in the pattern, i.e. bump structures made of the plating material inholes 110. It is contemplated that any suitable process besides platingcan be used for forming the bump structures, e.g., evaporationtechniques, without departing from the scope of this disclosure. Theplating material is only deposited in the holes 110, so the bumpstructures 116 are isolated from one another electrically, and arespaced apart from one another by the insulating material 102. Theplating material includes copper, indium, or any other suitable platingmaterial, e.g., for electrical conductivity.

Referring now to FIG. 6, the method includes removing the photo resistmaterial 114 after forming bump structures over the seed layer 112 andthe photo resist material 114. Removing the photo resist material 114can include leaving the bump structures 116 seated in a seat 122 of theseed layer 112. The remaining seed layer 112, i.e. the portions of seedlayer 112 remaining in FIG. 6 from what is left after removing theportions of seed layer 112 shown in FIG. 5 but removed in FIG. 6, isrecessed (as part of the removal of the photo resist material 114 ofFIG. 5) below the top surface 134 of insulating material 102 (asoriented in FIG. 6, in other words the surface of insulating material102 opposite wafer 104 and/or the bottoms surface 132 of holes 110 shownin FIG. 3), and below the surface 124 of the dielectric layer 106, toprovide a gap 118 between each bump structure 116 and the insulatingmaterial 102 at the top of each hole 110. A portion of each bumpstructure 116 extends from the seat 122 and proud of top surface 128 ofthe hole pattern.

A focal plane array assembled from a PDA and ROIC as described above candefine a plurality of pixels. The pixels can have a pitch size is lessthan 10 μm. The bump structures can each have a diameter less than 5 um.The bump structures can each have a height to diameter ratio of greaterthan 1:1.

The methods and systems of the present disclosure, as described aboveand shown in the drawings, provide for bump structures with superiorproperties including reduced bump size without short circuiting the bumpstructures in pressing. While the apparatus and methods of the subjectdisclosure have been shown and described with reference to preferredembodiments, those skilled in the art will readily appreciate thatchanges and/or modifications may be made thereto without departing fromthe scope of the subject disclosure.

What is claimed is:
 1. A system comprising: a layer of insulatingmaterial with holes therein; a seed layer seated within the holes,wherein the seed layer is recessed below a top surface of the insulatingmaterial that is opposite a bottom surface of the holes; and arespective bump structure seated in the seed layer of each hole.
 2. Thesystem as recited in claim 1, wherein the bump structures are on one ofa photodiode array (PDA) or a read-out integrated circuit (ROIC), andwherein the PDA and ROIC are joined together by the bump structures. 3.The system as recited in claim 2, wherein the PDA and ROIC define aplurality of pixels, wherein the plurality of pixels have a pitch size,wherein the pitch size is less than 10 μm.
 4. The system as recited inclaim 1, wherein the bump structures each have a diameter less than 5um.
 5. The system as recited in claim 1, wherein the bump structureseach have a height to diameter ratio of greater than 1:1.
 6. The systemas recited in claim 1, wherein a portion of the bump structures extendfrom the seed layer proud of the top surface of the insulating material.7. The system as recited in claim 1, further comprising a dielectriclayer on the top surface of the insulating material, wherein the seedlayer is recessed below the insulating material to provide a gap betweenthe bump structures and the insulating material, wherein the gap betweenthe bump structures and the insulating material is also between thedielectric layer and the bump structures.